This invention relates to a device for a vacuum cleaner having a suction nozzle and a dust bag, wherein the dust bag is connected to the suction nozzle, for instance, by means of a tube connection, and a turbo-fan unit is driven by an electric motor and placed after the dust bag, as seen in the direction of air flow. The impeller of the fan is driven at a speed above 50,000 rpm, and the primary air flow created by the unit leaves the unit via an outlet to atmosphere.
Vacuum cleaners of the above-mentioned type are described in WO 94/15518 and 94/15519, respectively, and mainly have the advantage that, because of the small dimensions of the vacuum source, they can be manufactured as small, hand-held appliances which are easy to handle and store while having suction power on the same level as previously known traditional vacuum cleaners, i.e., such having a power demand of between 500 and 1500 W.
In order to cool the electric motor in conventional vacuum cleaners the air flow, which is created by the fan and which is used for sucking up particles through the nozzle, is used. When the particles have been separated from the air in the dust bag and the air has passed through the fan, the air passes outside and through the electric motor before it exits the vacuum cleaner to atmosphere. This method of cooling the electric motor cannot be used in vacuum cleaners with small, high speed motors since the air which reaches the motor, despite the separation of the particles, is still dirty or contaminated, and can cause damage to the motor. It is a further risk in small, high speed motors that larger particles or details might follow the air flow into the motor if, for any reason, the dust bag would break, and that these particles would damage the motor due to the small dimensions of the motor and the narrow air passages provided therein.
Therefore, there exists a need in the art for a method of cooling small, high speed motors used in vacuum cleaners, and for a vacuum cleaner having a small, high speed motor which is cooled by an air stream independent of the primary dirt-laden air stream.